AQA BIOL5 ~ 17th June 2013 ~ A2 Biology

Hey! We went through this today in class from our mock & this is the mark scheme we were given from last year. My teacher said that they check you have something from a range from this table, to check you have breadth and knowledge, if that makes sense? Ask if it doesn't, my brain is a bit of a mess at explaining today :')




Posted from TSR Mobile

can someone help me on this please.in the menstrual cycle, it says that low oestrogen levels inhibit the release of FSH and LH but after 10 days it says that high levels of oestrogen stimulate the release of FSH and LH. why does this happen? I asked my teacher and she said you don't need to know why but I would like to understand myself why, becasue it just makes no sense to me!

Hey! We went through this today in class from our mock & this is the mark scheme we were given from last year. My teacher said that they check you have something from a range from this table, to check you have breadth and knowledge, if that makes sense? Ask if it doesn't, my brain is a bit of a mess at explaining today :')




Posted from TSR Mobile

But then does that mean if u have a topic from each of the 3 "big areas" you get all 3 Breadth marks? Or to get the 3 marks do u need every single topic in that mark scheme?

Basically, there is another hormone involved which actually stimulates FSH/LH production called gonadotrophin releasing hormone or GnRH (FSH and LH are gonadotrophins).GnRH is released from the hypothalamus and stimulates the production of FSH or LH from the pituitary gland depending on whether its released in "fast pulses" or "slow pulses".So, after the follicle is stimulated due to FSH production (from GnRH production) and oestrogen is released by it, oestrogen levels rise. Initially the rise in oestrogen has a negative feedback effect, by inhibiting GnRH release and so FSH production. When the oestrogen reaches its peak of concentration or goes above a certain critical level, it then stimulates GnRH production (and in this case both slow and fast pulses result in the production of LH and FSH). The result is a positive feedback effect, whereby LH "surges", causing ovulation.The exact mechanism of the switch from negative to positive feedback is apparently not well understood..but from what I have read, an increased level of responsiveness of the hypothalamus due to high oestrogen (and apparently progesterone levels) results in the positive feedback. I just think of it as a threshold level, whereby once you hit the oestrogen threshold, GnRH is like "I'm free!!!" so LH (and FSH) rise too because it stimulates their production.Hope that wasn't too deep! It all seems to be quite complex and there are a lot of factors contributing, so I think the textbook and teachers "dumb it down" so we stick to the key points.

This may sound like an extremely vague question, but can someone please explain the entire order of section 16? Our class has been given "independent study" for this section and I'm struggling to understand if there even is an order (e.g is 16.1 - 16.3 an order? As in, cut DNA > in vivo + marking OR in vitro > gets you the DNA you want for reasons said in 16.5?) I'll write what I mean below:

1. DNA needs to be isolated = which can be done by restriction endonucleases or reverse transcriptase
2. This provides a section of DNA that you want which needs to be cloned = which can be done by the PCR (in vitro) or by using vectors (in vivo)

I'm so confused as to whether this entire section is a sequence of events or all separate techniques... If someone would prefer to PM me in detail I would be sooo grateful. Independent study is the worst

Edit: I have another question... What determines whether a restriction endonucleases will cut in a blunt way or a staggered way? From what I can see, it's completely dependent on whichever random RE it is... So we wouldn't be asked to identify which way it would be cut, would we?

You've pretty much just got the idea there. You cut the section of DNA using restriction endonuclease or reverse transcriptase and then you can amplify the sample with PCR or vectors.

& Yes, its just dependent on the type of restriction enzyme so I highly doubt they can ask us how it would cut.

Basically, there is another hormone involved which actually stimulates FSH/LH production called gonadotrophin releasing hormone or GnRH (FSH and LH are gonadotrophins).

GnRH is released from the hypothalamus and stimulates the production of FSH or LH from the pituitary gland depending on whether its released in "fast pulses" or "slow pulses".

So, after the follicle is stimulated due to FSH production (from GnRH production) and oestrogen is released by it, oestrogen levels rise. Initially the rise in oestrogen has a negative feedback effect, by inhibiting GnRH release and so FSH production.

When the oestrogen reaches its peak of concentration or goes above a certain critical level, it then stimulates GnRH production (and in this case both slow and fast pulses result in the production of LH and FSH). The result is a positive feedback effect, whereby LH "surges", causing ovulation.

The exact mechanism of the switch from negative to positive feedback is apparently not well understood..but from what I have read, an increased level of responsiveness of the hypothalamus due to high oestrogen (and apparently progesterone levels) results in the positive feedback.

I just think of it as a threshold level, whereby once you hit the oestrogen threshold, GnRH is like "I'm free!!!" so LH (and FSH) rise too because it stimulates their production.

Hope that wasn't too deep! It all seems to be quite complex and there are a lot of factors contributing, so I think the textbook and teachers "dumb it down" so we stick to the key points.

This may sound like an extremely vague question, but can someone please explain the entire order of section 16? Our class has been given "independent study" for this section and I'm struggling to understand if there even is an order (e.g is 16.1 - 16.3 an order? As in, cut DNA > in vivo + marking OR in vitro > gets you the DNA you want for reasons said in 16.5?) I'll write what I mean below:

1. DNA needs to be isolated = which can be done by restriction endonucleases or reverse transcriptase
2. This provides a section of DNA that you want which needs to be cloned = which can be done by the PCR (in vitro) or by using vectors (in vivo)

I'm so confused as to whether this entire section is a sequence of events or all separate techniques... If someone would prefer to PM me in detail I would be sooo grateful. Independent study is the worst

Edit: I have another question... What determines whether a restriction endonucleases will cut in a blunt way or a staggered way? From what I can see, it's completely dependent on whichever random RE it is... So we wouldn't be asked to identify which way it would be cut, would we?

bloody hell, that's an excellent answer! thanks!

Breaking relevant news:



Rest of the article here:

Thought I could stop stalking bbc health after interviews Going to have to sub to new scientist again to get some ideas for the essay. Have you been revising earlier units?

Posted from TSR Mobile

When do you get double stranded RNA? like the ones that are cut up into siRNA